react/src/core/ReactEmptyComponent.js

/**
 * Copyright 2014, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule ReactEmptyComponent
 */

"use strict";

var ReactElement = require('ReactElement');

var invariant = require('invariant');

var component;
// This registry keeps track of the React IDs of the components that rendered to
// `null` (in reality a placeholder such as `noscript`)
var nullComponentIdsRegistry = {};

var ReactEmptyComponentInjection = {
  injectEmptyComponent: function(emptyComponent) {
    component = ReactElement.createFactory(emptyComponent);
  }
};

/**
 * @return {ReactComponent} component The injected empty component.
 */
function getEmptyComponent() {
  invariant(
    component,
    'Trying to return null from a render, but no null placeholder component ' +
    'was injected.'
  );
  return component();
}

/**
 * Mark the component as having rendered to null.
 * @param {string} id Component's `_rootNodeID`.
 */
function registerNullComponentID(id) {
  nullComponentIdsRegistry[id] = true;
}

/**
 * Unmark the component as having rendered to null: it renders to something now.
 * @param {string} id Component's `_rootNodeID`.
 */
function deregisterNullComponentID(id) {
  delete nullComponentIdsRegistry[id];
}

/**
 * @param {string} id Component's `_rootNodeID`.
 * @return {boolean} True if the component is rendered to null.
 */
function isNullComponentID(id) {
  return nullComponentIdsRegistry[id];
}

var ReactEmptyComponent = {
  deregisterNullComponentID: deregisterNullComponentID,
  getEmptyComponent: getEmptyComponent,
  injection: ReactEmptyComponentInjection,
  isNullComponentID: isNullComponentID,
  registerNullComponentID: registerNullComponentID
};

module.exports = ReactEmptyComponent;